Objective framework for selecting liquidity needs?

Im having trouble anticipating the correct liquidity needs and am hoping some of you guys have figured out the secret because it seems like it should be easy. I typically list any significant events known in advance that would require portions of the portfolio to be sold. Im noticing the past exams tend to be more specific.

For example, 2012 Q1 - D - i:

The question asks what liquidity needs have changed. I said the 250k for the trust is off the table and now he wont need to liquidate 1.6MM at retirement to buy the annuity. The key only included the 250k and said there were no other needs. Is it as simple as only selecting needs in the immediate term?

Yes, liquidity needs only concerns the next 12 months.